Introduction
Potassium (K), as one of the
three major nutrient elements to plants, plays an essential part in plant
physiological and biochemical processes (Marschner 2011). Due to K deficiency,
some metabolic activities and tolerance of plants are severely affected
(Pettigrew 2008; Shabala and Cuin 2008). Tobacco
(Nicotiana tabacum L.) is an important economic crop with about one
million acres each year in China. Potassium is crucial for tobacco leaves, and
the growth of tobacco depends mainly on its supply in the soil. It is not only
a critical nutrient element but also improves the flammability of flue-cured
tobacco and reduces the amount of tar produced in the combustion process (Zhang
and Kong 2014). It can also enhance tobacco identity, leaf color, aroma and
taste and so on (Liu et al. 2019). K content is one of the essential
factors affecting tobacco quality. Therefore, K acts as a
critical part of enhancing the yield and quality of agricultural production.
Potassium bacteria, also known as silicate
bacteria, are a kind of microorganism that can transform the potassium state
from unavailable to available. Besides, it can also release silicon,
phosphorus, and other elements for efficient absorption by plants. It is an
essential bacterium promoting the rhizosphere growth of extracellular plants.
According to statistics, there are approximately 2000~40000 potassium bacteria
in 1g cultivated soil (Zhang et al. 2017).
The K
content of high-quality tobacco leaves should not be less than 2%, but in most
tobacco areas of China, the K content is only 1~2% (Bao et al. 2015).
The lower K content of tobacco leaves restricts the further improvement of
tobacco quality. To solve these problems, among other methods, the use of some
organic products as soil amendments can promote the soil-plant relationship,
thus providing better K conditions in the K-deficiency period (Oram et al.
2014).
Table
1: Physicochemical properties of
experimental materials
|
Items |
Paddy soil |
Biochar |
|
BD (g cm-3) |
1.12 |
0.21 |
|
SSA (m2
g-1) |
15.4 |
|
|
OM (g kg-1) |
32.52 |
326.79 |
|
pH |
5.86 |
9.43 |
|
TP (g kg-1) |
0.49 |
2.51 |
|
AP (mg kg-1) |
27.67 |
1.09 |
|
TK (g kg-1) |
5.14 |
0.21 |
|
AK (mg kg-1) |
121.73 |
38.27 |
|
TN (g kg-1) |
1.32 |
0.043 |
Abbreviations: BD, bulk
density; SSA, specific surface area; OM, organic matter; TP, total phosphorus;
AP, available phosphorus; TK, total potassium; AK, available potassium; TN,
total nitrogen
CK = treatment without biochar;
C-5 = 5% biochar; C-10 = 10% biochar; C-15 = 15% biochar
Biochar
(BC) is formed by thermal transformation of waste biomass at high temperatures
under anaerobic or aerobic conditions, which is called pyrolysis (Brown 2012).
It can be served as a soil conditioner to better soil water and fertilizer
holding capacity and crop yield (Oram et al. 2014; Hussain et al. 2017; El-Naggar et al. 2019). Corn (Zea mays L.)
is a major food crop, with an annual straw output of more than 200 million tons
in China. Now, incineration is the most widely used method for corn straw
disposal, during which a large number of SO2, CO2 and other
toxic gases are released into the atmosphere, causing the severe air pollution
problem (Shi et al. 2014; Chi et al. 2017). Therefore, via the
anaerobic pyrolysis of corn straw to produce BC can attain the purpose of
recycling existing resources and energy, and avoid the severe air pollution hazard
caused by incineration.
In
this study, the pot experiments have been performed to conduct the influence of
the single application of BC on K absorption of tobacco with soil microbial and
chemical environments. The results of this study will not only provide
consultation for future research but also have a particular reference for the
manufacture and application of slow-release K fertilizer.
Materials
Corn straw gathered from Hunan
Agricultural University was used to produce the examined BC at 400–500°C, using
an electric BC reactor (Liu et al. 2016). Its primary physicochemical
properties are presented in Table 1.
Test crop and experimental
soils
Soil was collected from the
Farm of Hunan Agricultural University Cultivation Base in Changsha, Hunan,
China (113°08′N, 28°18′E). The fundamental properties of the soil
used in this study are given in Table 1. The tested flue-cured tobacco variety
was Yunyan 87, which has the characteristics of high quality, stable yield,
wide adaptability, strong stress resistance and easy curing (Li et al.
2001).
A pot experiment was carried
using the acidified paddy soils from 2016 to the end of 2018 in a plastic
greenhouse of Hunan Agricultural University. Plants were grown in laboratory
pot (18 cm upper diameter × 13 cm lower diameter ×14.5 cm deep) filled with 20
kg soil. Pot trial, a single-factor experiment with a completely randomized
design, was demonstrated to investigate the effects of the four BC amounts on
flue-cured tobacco and soil. Mulcahy's (Mulcahy et al. 2013) research
confirmed that the volume concentration required for BC to produce significant
biological effects is very high (15%). But Case et al. (2012) found that
adding low-level biochar (5 or 10%) to the surface soil can also improve the
property of the soil. Therefore, in this study following treatments as CK
(control without BC), C-5, C-10, and C-15, following the numbers denoting the
percentage of BC fortified were used. For each season, tobacco seeds were
cultivated in the seedling bed on May 1, and transplanted on May 15 with one
seedling per pot, and harvested in September. Experiment was laid out following
completely randomized design (CRD) and repeated 20 times.
After
tobacco harvesting, removed the remaining roots in the pot. To meet the needs
of crop normal growth and development carried out appropriate irrigation during
tobacco development according to weather and crop growth conditions. During the
growing stage, tobacco has put a unified management strategy. The amount of
fertilizer used in each treatment was the same. Recommended NPK fertilizers as
N, P2O5, and K2O (150, 90, 370 mg kg-1)
were applied as pure ammonium nitrate, potassium dihydrogen phosphate, and
potassium nitrate,
respectively.
After 25, 40, 55, 70 and 85
days of transplanting, three tobacco seedlings were randomly selected and
sampled. According to the survey method specified in the tobacco industry
standard, the tobacco growth parameters were determined in the harvesting time,
including plant height, effective leaf number, root length and fresh weight.
Then, in the time as mentioned above, plants were bagged according to the parts
of the root, stem, and leaf. The dry matter weight (DMW) of the corresponding
parts was determined by sterilizing at 105°C for 30 min and baking at 80°C
until constant weight. K content in tobacco leaves was determined by the
Laboratory Flow Analyser (PULSE3000) of the National Tobacco
Cultivation Physiological and Biochemical Base, referring to the standards of
the tobacco industry. Calculated K accumulation value (KAV) and at 85 days
after transplanting calculated K recovery efficiency (KRE).
At the
same time, soil samples were taken, left to dry naturally, and after 2 mm
sieve. The underlying properties of the soil were determined according to
Baoshidan's (Baoshidan 2000) ‘Soil Agrochemical Analysis’. Total potassium (TK)
determination using sodium hydroxide, flame photometry. Avail-K (AK) was
referred to as ammonium acetate leaching.
For
soil microorganisms, the number of K bacteria in soil samples was measured on 5
sampling days. K-solubilizing bacteria in rhizosphere soil were counted with
the silicate medium dilution plate method described by Razzaghi (Komaresofla et
al. 2019). The result, the number of rhizospheric K bacterial isolate, was
reported as colony–forming units (CFU) g−1 soil weight.
Calculation
The following parameters were
calculated based on dry matter weight (DMW) and the K concentrations in
different organs:
Where KUBC is K uptake in BC added
plot; KUCK is K uptake in no BC added plot; QKF is quantity of K
applied in each treatment.
Collected data were analyzed
using SPSS software (19.0 version of SPSS Company, Chicago, Illinois, U.S.A.)
to check the overall significance of data while Tukey test was used to compare
the treatments means at P < 0.05.
Plant growth parameters
Biochar application had
significant effect (P≤ 0.05) on plant height, root length and fresh
weight of tobacco plants and had non-significant effect on number of leaves
(Table 2). However, C-15 was found to be more effective to promote plant height
as it caused up to 3.36 and 1.65% increase over C-5 and C-10 treatment. For root
length, BC increased by 1.57–6.01 cm but did not reach a significant level.
Rhizosphere soil potassium bacteria
Fig. 1 shows that the BC
application significantly increased the soil K-bacteria number, and the
amplification rose with the increase of application amount. Compared with CK,
the growth rate of soil K bacteria in three consecutive years was 2.5–15.0%,
2.4–25.8% and 0.2–25.8%, respectively. It can be seen that the growth range
gradually decreases, and in the third year, there was no significant difference
between C-5 and CK. However, C-10 and C-15 were still significantly higher than
other treatments.
Soil potassium supply levels
The addition of BC has
significant influence (P < 0.05)
on available potassium (AK) in soils (Fig. 2). The AK in the BC-adapted soils
was 14.1–25.8% greater than CK in the first year, 15.2–64.8% greater in
the second year, and 9.5–61.6% greater in the third year.
On the
whole, in each period, the AK content of each treatment varied greatly. The treatments
with BC were significantly higher than CK, but there was no considerable
difference among the treatments of C-5, C-10, and C-15. The comprehensive
analysis performed that the BC implementation could improve soil K supply
levels, but the content of AK in soil did not rise considerably.
K recovery efficiency (KRE)
After applying BC, KRE
increased more substantially with the amount increasing (Fig. 3). The KRE of
different BC amount treatments varied greatly, especially C-15 treatment, which
reached 34.70%, low and median BC treatments were 12.11% and 22.80%,
respectively. In the second year, compared to 2016, KRE increased by 66.0% in
C-15 and 62.5% in C-10, and 50.1% in C-5. In the last year, compared to 2017,
KRE decreased by 45.6% in C-5 and 19.8% in C-10, while only 4.4% in C-15.
K accumulation and distribution
dynamics of plants
From Fig. 4, it can be seen
that the trend of K accumulation in tobacco plants added BC is the same as the
CK, increasing by about 13%. However, after maturity (transplanting days >
70d), K can’t still be absorbed and accumulated at a higher rate, even
declined, while the dry matter of tobacco plants continues to accumulate.
During this period, the K accumulation in tobacco plants decreased by 65%.
In the
second year, compared with 2016, the rates of K uptake and accumulation of
tobacco plants with BC were speeded up, while the gap with CK was gradually
increased from 0.9 to 2.8 g/plant. In the third year, there was almost no
significant difference, but it still performs C-15>C-10>C-5>CK.
With
the development of tobacco, the K proportion in tobacco leaves increased first
and then decreased, especially after maturity, decreased to 65.6%, while the
percentage in stems showed a gradual upward tendency (Table 3). Treatments with
BC speeded up this trend and favorable to root growth. Over the three years, at
85d after transplanting, the proportion of K in industrial products is
relatively high, accounting for 65.6–78.1%
of the total potassium uptake, while the proportion of K in non-economic
products is relatively low, accounting for only 21.9–34.4%.
In non-economic products, stem and root account for a considerable proportion,
indicating that the distribution of K in non-BC treatment is more reasonable
during the first two years, but it is more consistent in BC treatments in the
last year.
BC application improved
tobacco growth (Table 2) due to significant improvement in K
availability. Potassium is a crucial nutrient for plant growth and
development (Manzoor et al. 2018). From 90 to 98% of K in the
soil exists in various soil minerals and sedimentary
materials (Parmar and Sindhu 2013), which cannot be dissolved and absorbed
directly by plants. Numerous studies have shown that there are a variety of
K-solubilizing bacteria in the soil (Dong et al. 2019). These can
promote the transformation of insoluble K and other nutrients into soluble
nutrients, which can be immediately uptake by crops, and secrete active
substances to improve crop growth, which has an essential contribution
to plant absorption (Basak and Biswas 2008).
Table 2: Effect
of biochar application on plant height, number of leaves, root length and root
fresh weight of tobacco plants
|
Year |
Treatments |
Plant height (cm) |
Number of leaves per
plant |
Root length (cm) |
Root fresh weight (g
plant-1) |
|
2016 |
CK |
98.0 ± 0.00b |
15.7 ± 0.47NS |
30.34 ± 0.55b |
270.43 ± 8.56b |
|
C-5 |
98.7 ± 0.47ab |
16.0 ± 0.00 |
32.38 ± 1.94a |
277.29 ± 5.27ab |
|
|
C-10 |
99.3 ± 0.47a |
16.3 ± 0.47 |
35.85 ± 2.49a |
283.95 ± 4.06ab |
|
|
C-15 |
97.0 ± 0.00c |
16.3 ± 0.47 |
36.35 ± 3.74a |
287.21 ± 5.04a |
|
|
2017 |
CK |
97.7 ± 0.47d |
15.7 ± 0.47 |
31.02 ± 2.78a |
275.71 ± 10.61b |
|
C-5 |
99.3 ± 0.47c |
16.0 ± 0.82 |
33.83 ± 2.87a |
285.24 ± 3.69b |
|
|
C-10 |
101.0 ± 0.82b |
15.7 ± 0.47 |
35.08 ± 3.49a |
291.03 ± 4.00ab |
|
|
C-15 |
102.7 ± 0.47a |
16.3 ± 0.47 |
36.78 ± 2.42a |
302.93 ± 6.00a |
|
|
2018 |
CK |
93.2 ± 0.24c |
15.3 ± 0.94 |
30.87 ± 4.92a |
273.49 ± 3.03b |
|
C-5 |
95.7 ± 0. 62b |
15.3 ± 0.47 |
32.44 ± 3.42a |
282.51 ± 5.89ab |
|
|
C-10 |
96.5 ± 0.41ab |
16.0 ± 0.00 |
34.43 ± 4.74a |
286.07 ± 7.41a |
|
|
C-15 |
97.3 ± 0.47a |
16.3 ± 0.47 |
36.32 ± 3.18a |
291.71 ± 3.71a |
Means ± standard deviation
sharing same letters differ non-significantly (P > 0.05)
CK = treatment without biochar;
C-5 = 5% biochar; C-10 = 10% biochar; C-15 = 15% biochar
Fig. 1: Effect of biochar application on
potassium bacteria in rhizosphere soil during different growth periods
CK =treatment without biochar; C5 = treatment with 5%
biochar; C10 = treatment with 10% biochar; C15 = treatment with 15% biochar.
Each histogram is mean value of 3 replications ± S.E, where vertical bars
different letters on bars are showing statistical differences at P ≤ 0.05
represent the standard deviation of means each treatment (n=3)
Fig. 2: Effect of biochar application on the available potassium during
different growth periods
CK
=treatment without biochar; C5 = treatment with 5% biochar; C10 = treatment
with 10% biochar; C15 = treatment with 15% biochar. Each histogram is mean
value of 3 replications ± S.E, where vertical bars different letters on bars
are showing statistical differences at P ≤ 0.05 epresent the standard
deviation of means each treatment (n=3)
Fig. 3: Effect of biochar application on potassium recovery
efficiency (KRE)
C5 = treatment with 5% biochar; C10 = treatment with 10%
biochar; C15 = treatment with 15% biochar. Each dot is mean value of 3
replications ± S.
Table 3: Effect of biochar application on K absorption and distribution in tobacco at
different transplanting days in three years
|
Year |
Days after transplanting
(d) |
Treatments |
Root (g plant-1) |
Distribution ratio (%) |
Stem (g plant-1) |
Distribution ratio (%) |
Leaf (g plant-1) |
Distribution ratio (%) |
Whole K+ (g plant-1) |
|
2016 |
25 |
CK |
0.05 ± 0.00a |
5.29 |
0.28 ± 0.03a |
27.74 |
0.67 ± 0.08a |
66.97 |
1.00 ± 0.05a |
|
C-5 |
0.04 ± 0.00b |
4.76 |
0.25 ± 0.01ab |
28.44 |
0.59 ± 0.07a |
66.80 |
0.88±0.07ab |
||
|
C-10 |
0.04 ± 0.00ab |
5.30 |
0.20 ± 0.01b |
24.40 |
0.57 ± 0.18a |
70.29 |
0.81±0.18ab |
||
|
C-15 |
0.04 ± 0.00b |
5.11 |
0.20 ± 0.04b |
27.27 |
0.50 ± 0.06a |
67.62 |
0.74 ± 0.07b |
||
|
40 |
CK |
0.26 ± 0.02b |
8.12 |
0.67 ± 0.29a |
21.13 |
2.26 ± 0.23a |
70.74 |
3.19 ± 0.07a |
|
|
C-5 |
0.33 ± 0.01a |
11.07 |
0.75 ± 0.32a |
25.57 |
1.87 ± 0.09b |
63.36 |
2.94 ± 0.42a |
||
|
C-10 |
0.33 ± 0.01a |
11.85 |
0.60 ± 0.29a |
21.56 |
1.86 ± 0.05b |
66.59 |
2.79 ± 0.33a |
||
|
C-15 |
0.31 ± 0.01a |
10.98 |
0.70 ± 0.33a |
24.72 |
1.81 ± 0.08b |
64.30 |
2.81 ± 0.32a |
||
|
55 |
CK |
0.54 ± 0.02b |
8.87 |
1.61 ± 0.02a |
26.31 |
3.97 ± 0.08a |
64.82 |
6.12 ± 0.10a |
|
|
C-5 |
0.69 ± 0.04a |
10.96 |
1.74 ± 0.07a |
27.43 |
3.90 ± 0.13a |
61.60 |
6.33 ± 0.21a |
||
|
C-10 |
0.75 ± 0.05a |
12.02 |
1.61 ± 0.06a |
25.95 |
3.85 ± 0.04a |
62.03 |
6.21 ± 0.03a |
||
|
C-15 |
0.78 ± 0.03a |
12.66 |
1.69 ± 0.05a |
27.45 |
3.68 ± 0.47a |
59.89 |
6.15 ± 0.49a |
||
|
70 |
CK |
0.39 ± 0.03b |
4.12 |
2.34 ± 0.05b |
24.65 |
6.76 ± 0.12b |
71.22 |
9.49 ± 0.08b |
|
|
C-5 |
0.39 ± 0.01b |
3.93 |
2.38 ± 0.04b |
24.11 |
7.11 ± 0.29b |
71.96 |
9.87 ± 0.29b |
||
|
C-10 |
0.46 ± 0.06ab |
4.18 |
2.58 ± 0.02a |
23.54 |
7.91 ± 0.21a |
72.27 |
10.94±0.27a |
||
|
C-15 |
0.54 ± 0.05a |
5.05 |
2.32 ± 0.11b |
21.69 |
7.84 ± 0.06a |
73.26 |
10.71±0.14a |
||
|
85 |
CK |
0.13 ± 0.01b |
2.30 |
1.51 ± 0.05c |
26.67 |
4.03 ± 0.11a |
71.03 |
5.68 ± 0.14b |
|
|
C-5 |
0.14 ± 0.01b |
2.28 |
1.53 ± 0.02c |
24.90 |
4.49 ± 0.38a |
72.82 |
6.16±0.37ab |
||
|
C-10 |
0.18 ± 0.02ab |
2.86 |
1.71 ± 0.06b |
26.88 |
4.47 ± 0.28a |
70.26 |
6.36 ± 0.35a |
||
|
|
|
C-15 |
0.23 ± 0.04a |
3.46 |
1.88 ± 0.04a |
28.38 |
4.51 ± 0.06a |
68.16 |
6.62 ± 0.07a |
|
2017 |
25 |
CK |
0.07 ± 0.00a |
8.14 |
0.24 ± 0.02a |
26.88 |
0.59 ± 0.08a |
64.98 |
0.91 ± 0.07a |
|
C-5 |
0.08 ± 0.02a |
7.96 |
0.28 ± 0.03a |
28.44 |
0.62 ± 0.10a |
63.60 |
0.97 ± 0.10a |
||
|
C-10 |
0.07 ± 0.02a |
6.93 |
0.28 ± 0.08a |
28.97 |
0.63 ± 0.25a |
64.09 |
0.98 ± 0.36a |
||
|
C-15 |
0.07 ± 0.03a |
6.20 |
0.33 ± 0.09a |
31.79 |
0.65 ± 0.25a |
62.02 |
1.05 ± 0.37a |
||
|
40 |
CK |
0.35 ± 0.04a |
12.14 |
0.71 ± 0.45a |
24.47 |
1.83 ± 0.13b |
63.40 |
2.88 ± 0.41a |
|
|
C-5 |
0.46 ± 0.08a |
13.46 |
0.80 ± 0.52a |
23.51 |
2.14 ± 0.11a |
63.03 |
3.39 ± 0.62a |
||
|
C-10 |
0.46 ± 0.02a |
13.60 |
0.79 ± 0.16a |
23.39 |
2.12 ± 0.06a |
63.02 |
3.36 ± 0.19a |
||
|
C-15 |
0.44 ± 0.11a |
12.37 |
0.84 ± 0.31a |
23.49 |
2.31 ± 0.10a |
64.13 |
3.59 ± 0.17a |
||
|
55 |
CK |
0.53 ± 0.06a |
7.59 |
1.85 ± 0.35a |
26.35 |
4.65 ± 0.05d |
66.06 |
7.04 ± 0.35b |
|
|
C-5 |
0.66 ± 0.17a |
8.04 |
1.96 ± 0.23a |
23.82 |
5.60 ± 0.03b |
68.14 |
8.22 ± 0.30a |
||
|
C-10 |
0.74 ± 0.07a |
9.02 |
2.15 ± 0.21a |
26.19 |
5.31 ± 0.05c |
64.79 |
8.19 ± 0.15a |
||
|
C-15 |
0.61 ± 0.02a |
6.98 |
2.09 ± 0.23a |
24.06 |
5.99 ± 0.04a |
68.96 |
8.68 ± 0.23a |
||
|
70 |
CK |
0.75 ± 0.01b |
6.94 |
2.42 ± 0.12b |
22.52 |
7.59 ± 0.24c |
70.54 |
10.75±0.34c |
|
|
C-5 |
0.95 ± 0.05ab |
7.26 |
2.63 ± 0.10b |
20.20 |
9.46 ± 0.12b |
72.55 |
13.03±0.21b |
||
|
C-10 |
1.18 ± 0.19a |
7.95 |
3.47 ± 0.26a |
23.37 |
10.20 ± 0.30a |
68.68 |
14.86±0.47a |
||
|
C-15 |
0.93 ± 0.04b |
6.39 |
3.70 ± 0.17a |
25.40 |
9.95 ± 0.09a |
68.21 |
14.58±0.08a |
||
|
85 |
CK |
0.10 ± 0.03c |
1.88 |
1.41 ± 0.10c |
25.28 |
4.06 ± 0.07d |
72.84 |
5.58 ± 0.13d |
|
|
C-5 |
0.38 ± 0.03b |
5.80 |
1.67 ± 0.13c |
25.49 |
4.50 ± 0.02c |
68.71 |
6.55 ± 0.11c |
||
|
C-10 |
0.32 ± 0.05b |
4.26 |
2.01 ± 0.24b |
27.17 |
5.07 ± 0.07b |
68.57 |
7.40 ± 0.32b |
||
|
C-15 |
0.50 ± 0.07a |
5.98 |
2.37 ± 0.03a |
28.41 |
5.48 ± 0.15a |
65.61 |
8.35 ± 0.18a |
||
|
2018 |
25 |
CK |
0.05 ± 0.00a |
6.83 |
0.22 ± 0.03a |
27.68 |
0.51 ± 0.03a |
65.49 |
0.78 ± 0.06a |
|
C-5 |
0.05 ± 0.02a |
6.89 |
0.22 ± 0.02a |
28.19 |
0.51 ± 0.03a |
64.92 |
0.79 ± 0.01a |
||
|
C-10 |
0.06 ± 0.01a |
7.11 |
0.23 ± 0.02a |
28.02 |
0.53 ± 0.05a |
64.87 |
0.81 ± 0.06a |
||
|
C-15 |
0.06 ± 0.02a |
6.93 |
0.25 ± 0.04a |
29.11 |
0.55 ± 0.03a |
63.96 |
0.86 ± 0.01a |
||
|
40 |
CK |
0.24 ± 0.01b |
10.17 |
0.61 ± 0.03b |
26.25 |
1.48 ± 0.01c |
63.58 |
2.33 ± 0.03d |
|
|
C-5 |
0.26 ± 0.01b |
10.08 |
0.64 ± 0.02b |
24.66 |
1.68 ± 0.02b |
65.26 |
2.58 ± 0.02c |
||
|
C-10 |
0.32 ± 0.02a |
11.89 |
0.65 ± 0.02b |
24.26 |
1.72 ± 0.03b |
63.85 |
2.69 ± 0.05b |
||
|
C-15 |
0.34 ± 0.00a |
11.68 |
0.72 ± 0.04a |
24.99 |
1.83 ± 0.04a |
63.33 |
2.89 ± 0.07a |
||
|
55 |
CK |
0.25 ± 0.01d |
4.99 |
1.46 ± 0.02b |
28.69 |
3.39 ± 0.14b |
66.32 |
5.11 ± 0.13c |
|
|
C-5 |
0.33 ± 0.01c |
6.65 |
1.49 ± 0.04b |
29.95 |
3.16 ± 0.19b |
63.40 |
4.99 ± 0.14c |
||
|
C-10 |
0.44 ± 0.01b |
7.54 |
1.54 ± 0.04b |
26.40 |
3.85 ± 0.20a |
66.06 |
5.83 ± 0.18b |
||
|
C-15 |
0.51 ± 0.03a |
7.93 |
1.70 ± 0.09a |
26.54 |
4.20 ± 0.18a |
65.53 |
6.42 ± 0.25a |
||
|
70 |
CK |
0.22 ± 0.03c |
3.11 |
1.62 ± 0.06b |
23.46 |
5.07 ± 0.09d |
73.42 |
6.91 ± 0.11d |
|
|
C-5 |
0.27 ± 0.03c |
3.53 |
1.58 ± 0.03b |
20.50 |
5.87 ± 0.05c |
75.97 |
7.72 ± 0.10c |
||
|
C-10 |
0.50 ± 0.02b |
5.45 |
1.80 ± 0.08a |
19.56 |
6.90 ± 0.08b |
74.99 |
9.20 ± 0.17b |
||
|
C-15 |
0.61 ± 0.05a |
6.14 |
1.94 ± 0.10a |
19.71 |
7.30 ± 0.16a |
74.15 |
9.85 ± 0.23a |
||
|
85 |
CK |
0.08 ± 0.03c |
1.58 |
1.19 ± 0.06c |
23.89 |
3.71 ± 0.08b |
74.53 |
4.97 ± 0.10b |
|
|
C-5 |
0.10 ± 0.01bc |
1.73 |
1.14 ± 0.09c |
20.18 |
4.40 ± 0.28ab |
78.09 |
5.64 ± 0.21b |
||
|
C-10 |
0.18 ± 0.04b |
2.76 |
1.49 ± 0.05b |
22.94 |
4.83 ± 0.33ab |
74.30 |
6.50±0.30ab |
||
|
C-15 |
0.35 ± 0.06a |
4.54 |
1.72 ± 0.05a |
22.57 |
5.56 ± 1.21a |
72.89 |
7.63 ± 1.19a |
Means ± standard deviation
sharing same letters differ non-significantly (P > 0.05)
CK = treatment without biochar;
C-5 = 5% biochar; C-10 = 10% biochar; C-15 = 15% biochar
Fig. 4: Effect of biochar application on tobacco K accumulation
curve
CK =treatment without biochar;
C5 = treatment with 5% biochar; C10 = treatment with 10% biochar; C15 =
treatment with 15% biochar. Each dot is mean value of 3 replications ± S.E
In this study, after three
years of research and one-time BC use, the number of K bacteria in tobacco
planting soil significantly increased, which was consistent with the previous
research results (Zheng et al. 2019). Chen and Du (2015) also found that
the application of BC increased the amount of K bacteria in tobacco field soil
by 16.1%.
In the
present study, AK and KAV were greatly raised over three years in the soil
backing the C-15 compared to CK. This phenomenon can be explained by the
application of BC to increase the number of soil potassium bacteria and tobacco
root growth. The findings also confirm the latest survey by Singh et al. (2019), who discovered a
remarkable extension in soil AK after BC incorporation thanks to its
characterization. The characterization describes the mechanism at the back of
soil K adsorption in paddy soils owing to BC’s porosity and interplay with clay
minerals. BC addition provoked an increment in net mineralization of K in soil,
while as well as adsorbing mineralized K and K bacteria onto the pore rooms and
the surface area of BC. Therefore, the porous structure of BC can improve the
soil porosity and bulk density, enhance the surface area of soil, increase K
bacteria quantitative, accelerate the mineralization and the release of slowly
available potassium, and enhance K supply capacity (Asai et al. 2009).
Thus, it is beneficial to the increase of KAV. This discovery is hoped for
having a noteworthy impact on K recovery advancement and K concentration
enhancement in tobacco. This, in turn, will bode well for future agricultural
behavior to lessen the loss of K to erosion from cultivated lands and to
provide the beneficial ecosystem benefits.
Furthermore,
increased soil aggregate stability in acidic tropical soils (Hartley et al.
2016; Zhang et al. 2019) as moderated by BC modification plausibly
donated dramatically to enhance K concentration. Also, BC adjustment may induce
changes in soil quality, thereby modifying soil K forms.
BC adjustment created a
profound transformation in the chemical and microbial ecology of the paddy soil
together with the tobacco growth. BC applied in this study showed a good
application potential to improve the soil K contents, but the results of this
experiment were obtained under the condition of potting. The mechanism of BC
and its field application effect need further study.
This study was supported by the Chenzhou tobacco company project (Grant No.
2019-GL-16) and Changsha tobacco company project (Grant No. 2018430100270154).
The authors have declared no conflict of interest. We thank the help of the
Agronomy College of Hunan Agricultural University.
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